From fd9d9effda91bdba9b9135ef8b66f14bb576dc25 Mon Sep 17 00:00:00 2001
From: Daniel Lemire <daniel@lemire.me>
Date: Wed, 16 Nov 2022 15:25:03 -0500
Subject: [PATCH] More tweaking around clangcl

---
 include/fast_float/parse_number.h | 13 +++--
 tests/basictest.cpp               | 91 +++++++++++++++++++++++--------
 2 files changed, 75 insertions(+), 29 deletions(-)

diff --git a/include/fast_float/parse_number.h b/include/fast_float/parse_number.h
index b5f92ce..2b3b935 100644
--- a/include/fast_float/parse_number.h
+++ b/include/fast_float/parse_number.h
@@ -135,13 +135,14 @@ from_chars_result from_chars_advanced(const char *first, const char *last,
     // We do not have that fegetround() == FE_TONEAREST.
     // Next is a modified Clinger's fast path, inspired by Jakub Jelínek's proposal
     if (pns.exponent >= 0 && pns.exponent <= binary_format<T>::max_exponent_fast_path() && pns.mantissa <=binary_format<T>::max_mantissa_fast_path(pns.exponent) && !pns.too_many_digits) {
-#if (defined(_WIN32) && defined(__clang__))
-      // 32-bit ClangCL maps 0 to -0.0 when fegetround() == FE_DOWNWARD
-      value = pns.mantissa ? T(pns.mantissa) : 0.0;
-#else
-      value = T(pns.mantissa);
+#if (defined(_MSC_VER) && defined(__clang__))
+      // ClangCL may map 0 to -0.0 when fegetround() == FE_DOWNWARD
+      if(pns.mantissa == 0) {
+        value = 0;
+        return answer;
+      }
 #endif
-      value = value * binary_format<T>::exact_power_of_ten(pns.exponent);
+      value = T(pns.mantissa) * binary_format<T>::exact_power_of_ten(pns.exponent);
       if (pns.negative) { value = -value; }
       return answer;
     }
diff --git a/tests/basictest.cpp b/tests/basictest.cpp
index 1c07256..fec51de 100644
--- a/tests/basictest.cpp
+++ b/tests/basictest.cpp
@@ -48,13 +48,66 @@
 #define fHexAndDec(v) std::hexfloat << (v) << " (" << std::defaultfloat << (v) << ")"
 
 
-// C++ 17 because it is otherwise annoying to browse all files in a directory.
-// We also only run these tests on little endian systems.
-#if (FASTFLOAT_CPLUSPLUS >= 201703L) && (FASTFLOAT_IS_BIG_ENDIAN == 0) && !defined(FASTFLOAT_ODDPLATFORM)
+const char * round_name(int d) {
+  switch(d) {
+    case FE_UPWARD:
+      return "FE_UPWARD";
+    case FE_DOWNWARD:
+      return "FE_DOWNWARD";
+    case FE_TOWARDZERO:
+      return "FE_TOWARDZERO";
+    case FE_TONEAREST:
+      return "FE_TONEAREST";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+
+#define FASTFLOAT_STR(x)   #x
+#define SHOW_DEFINE(x) printf("%s='%s'\n", #x, FASTFLOAT_STR(x))
+
+TEST_CASE("system_info") {
+    std::cout << "system info:" << std::endl;
+#ifdef _MSC_VER
+    SHOW_DEFINE(_MSC_VER);
+#endif
+#ifdef FASTFLOAT_64BIT_LIMB
+    SHOW_DEFINE(FASTFLOAT_64BIT_LIMB);
+#endif
+#ifdef __clang__
+    SHOW_DEFINE(__clang__);
+#endif
+#ifdef FASTFLOAT_VISUAL_STUDIO
+    SHOW_DEFINE(FASTFLOAT_VISUAL_STUDIO);
+#endif
+#ifdef FASTFLOAT_IS_BIG_ENDIAN
+    #if FASTFLOAT_IS_BIG_ENDIAN
+      printf("big endian\n");
+    #else
+      printf("little endian\n");
+    #endif
+#endif
+#ifdef FASTFLOAT_32BIT
+    SHOW_DEFINE(FASTFLOAT_32BIT);
+#endif
+#ifdef FASTFLOAT_64BIT
+    SHOW_DEFINE(FASTFLOAT_64BIT);
+#endif
+#ifdef FLT_EVAL_METHOD
+    SHOW_DEFINE(FLT_EVAL_METHOD);
+#endif
+#ifdef _WIN32
+    SHOW_DEFINE(_WIN32);
+#endif
+#ifdef _WIN64
+    SHOW_DEFINE(_WIN64);
+#endif
+    std::cout << "fegetround() = " << round_name(fegetround()) << std::endl;
+    std::cout << std::endl;
+
+}
 
-#include <iostream>
-#include <filesystem>
-#include <charconv>
 
 TEST_CASE("rounds_to_nearest") {
   //
@@ -82,23 +135,6 @@ TEST_CASE("rounds_to_nearest") {
   CHECK(fast_float::detail::rounds_to_nearest() == true);
 }
 
-const char * round_name(int d) {
-  switch(d) {
-    case FE_UPWARD:
-      return "FE_UPWARD";
-    case FE_DOWNWARD:
-      return "FE_DOWNWARD";
-    case FE_TOWARDZERO:
-      return "FE_TOWARDZERO";
-    case FE_TONEAREST:
-      return "FE_TONEAREST";
-    default:
-      return "UNKNOWN";
-  }
-
-}
-
-
 TEST_CASE("parse_zero") {
   //
   // If this function fails, we may be left in a non-standard rounding state.
@@ -146,6 +182,15 @@ TEST_CASE("parse_zero") {
   CHECK(float64_parsed == 0);
 }
 
+// C++ 17 because it is otherwise annoying to browse all files in a directory.
+// We also only run these tests on little endian systems.
+#if (FASTFLOAT_CPLUSPLUS >= 201703L) && (FASTFLOAT_IS_BIG_ENDIAN == 0) && !defined(FASTFLOAT_ODDPLATFORM)
+
+#include <iostream>
+#include <filesystem>
+#include <charconv>
+
+
 
 // return true on success
 bool check_file(std::string file_name) {